/me throws my pennies on the table
Not going to single out posts... just add my pennies to the pile :)
1) A 24-pin PS that has seperate wires going all the way back to the PCB in the PS IS a 24-pin PS. It is not a "re-treaded 20-pin supply".
2) On the issue of seperate +12V rails - this is about compliance with certain governmental regulations in various locals and has nothing to do with a PS being a 24-pin PS nor with it meeting the requirements of a ATX 2.0x supply.
3) The extra 4 pins on a 24-pin PS is not just about current carrying capabilities and/or extra pins. It also involves issues of parasitics in the power distribution system for your MB and add-in cards... including IR drop, inductance, frequency response, and noise. It also has to do with compliance to the ATX 2.x specs. And it requires seperate connections all the way back to the PS.
4) Based upon my own design experience, there are valid reasons why DFI is requiring true 24-pin PS's. See comment 3.
5) It is possible with a good 20-pin PS to create the equivalent of a 24-pin PS using a 24 to 20 pin adapater - it's done by cutting the wires between the extra four pins of the adapter at the point they join the standard 20-pin power pins and connecting the now unconnected 4 extra pins' wires all the way back to the PS's PWB with their own seperate wires. One way to do this is to use one of the SATA power connectors, which has all 4 required connections (+5,+12,+3.3,Gnd) and seperate wires all the way back.
6) I initially ran my DFI NF4 with a 20-pin PCPnC 450ATX supply without any problems on my bench (although in a stripped system configuration). But... it did hinder the performance. Whether or not a 20-pin PSU can work depends on the PS, what other components are in the system, and how close to the edge you intend to push your system.
So in regards to can you use a 20-pin PSU... given certain conditions, yes. Will it provide you with the most stable, overclockable system without at least modification as discussed in comment 5....NO. Does DFI know what it's talking about making a 24-pin PS a requirement...YES! For much the same reasons, plugging the extra MB power connectors into your PS is also recommended.
By way of a recent experience (one of many, many, many dealing with power and power distribution issues I've seen), maybe you'll understand DFI's stance on this issue....
On a project I'm working on at work, we had performed exhaustive testing on some new hardware and it had performed flawlessly in our development test environment. When we did a manufacturing run of the item in question, they were "failing" during manufacturing testing. I ended up during a 72 hour period, with only two 3 hour stints of sleep intermixed, in the manufacturing facility tracking down WTH was going on (and then lending a helping hand to testing to meet our deadline). To make a long story shorter, the problem ended up being someone who thought they could disregard the guidelines I had given regarding the power distribution in the test setup and used single wire connections between the test station power supplies and the test adapter for power distribution, along with improper power distribution inside the test adapter. The net result was perfectly good products with excellent margins "failing" test and my aforementioned grueling 3 days isolating, identifying, proving, and fixing the test setup they were using so that it conformed to the initially stated requirements. Afterwards the batch of product passed all testing with flying colors and substantial margins and are now being happily used by the customer :D
Oh... one last comment... it is *possible* under certain conditions for what the OCZ rep said to occur...
Don't ask if you don't really want to know, lol
Quote:
Originally Posted by Krohling
But in the DFI LP UT NF4 Ultra-D motherboard, the connections between the +12V, +5V, +3.3V and Ground are phisically connected to the other regular 12V input, 5V input, etc
Correct :)
Quote:
Originally Posted by Krohling
how would a 24 pin PSU act different, you would cause a short circuit between the first 12V line, and the other 12V line?
No, I am aware of no PS's which have seperate output rails for the extra 4 connections of a 24-pin connector.
First an observation - just because different connections are electrically the same (read basically short across a conventional DMM), does not mean that they are all tied into the same power planes, and in fact could be tied to seperate planes that are only referenced together through a single via or trace (don't know if this is the case in the DFI Nf4 or not for any of the rails).
But... the difference is as a result of what I previously commented on - it deals with IR drops, trace inductance, frequency response (yes, power distribution systems have frequency response components), and noise issues - also known as the real world of electronics and parasitic reactances.
To give an example of how it likely could make a difference in the specific case of the DFI motherboard....
Present day CPUs and memory and GPUs all have very high transient current requirements (i.e. the current they require can change quite rapidly by a considerable amount in very short time frames measured in milli-seconds and even micro and nano-seconds). Up to a limit, determined by the amount and quality of the decoupling of the power locally (i.e. on the MB, DIMM, or Gfx card), this can cause a drop in the supply rails under certain conditions.
Normally the local decoupling (provided by capacitors, which store charge and resist changes to voltage caused by changing current demands) handles these temporary requirements.... BUT... there is a limit after which they "run out of charge" and can no longer supply the extra power being demanded. At that point, the supply rail starts dropping rather rapidly - not a good thing at all. To prevent this occurence, there must exist the capability to supply more current from the power supply before the capacitors stop compensating for the increased current demand. This is where that 24-pin connector (and the type of wiring used between it and the PS) can make a big difference.
Each wire between the power supply and the MB has inherent parasitic values - it isn't a 0 ohm, 0 inductance connection. The first of these is resistance. If the resistance is too high, the increased temporary current demand can cause a drop in the input voltage being supplied - causing the situation to worsen. The resistance in the wires also affects the amount of time it takes to replenish the charge of the onboard capacitors - possibly leading to their inability to handle the next transient current demand if it comes soon enough.... or maybe the 3rd one, etc.. or maybe just in those instances when everybody is depending increased current all at once - leading to those "pretty" windows BSODs.
The other aspect of the wire is that it has inductance. Inductance is a material's (the wires in this case) "resistance" to a change in current (versus the capacitors "resistance" to a change in voltage). Note that in the case of both capacitance and inductance this "resistance" (properly called impedance) is dependent on frequency. Now inductance can be either beneficial or detrimental to a circuit, depending upon the circuit (as can capacitance). In the case of power distribution (not power conditioning or conversion) inductance has a pronounced negative affect. When that sudden large change in current requirement occurs, the inductance of the wire resists the change and causes a lag in time before the increase in current demand can be met by the power supply.
In regards to how it affects noise - the overall impedance (the frequency dependant resistance of a component or system) determines the amount of noise coupling between two seperate, but adjacent, circuits. The lower the impedance of a connection, the smaller the magnitude of noise that will be coupled to it by an adjacent circuit. Increased inductance and resistance (in the case of no real net change in capacitance) causes the impedance to be higher - causing more noise to be coupled, in this case to the connections between the power supply and the MB.
And the last piece of the puzzle as it were... in the case of both resistance and inductance... when you parallel components (in this case the wires) with these characteristics, the result is a decrease in the net (total) value. Put two resistors or inductors of equal value in parallel and the value is halved. Put 3 in parallel and the value is reduced to 1/3rd. etc., etc.
And of course... the actual connector pins themselves also have these same circuit properties as well.
So, by adding the extra wires and connector pins between the power supply and the MB, the transient response characteristics of the power distribution system is improved, as is the noise characteristics, leading to cleaner, more stable power for all those OC'd goodies on your MB ;)
Hope that answers your Q :D
Peace :toast:
